Hybrid twin coil electrical machine

ABSTRACT

A hybrid electrical machine having a permanent magnetic rotor field in addition to an electrically excited rotor field is disclosed. The generator rotor ( 220 ) has two opposing claw segments ( 226, 228 ) mounted at opposite ends of a rotor shaft ( 222 ). A third, center claw segment ( 232 ) is mounted on the rotor shaft between the first and second claw segments. A first wound field coil ( 224 ) is mounted on the rotor shaft between the first and third claw segments, and a second wound field coil ( 234 ) is mounted between the second and third claw segments. One or more permanent magnets ( 230, 231 ) may be provided about the periphery of the first, second, and/or third claw segments.

BACKGROUND OF THE INVENTION

1. The Technical Field

The invention relates generally to electrical machines, such as motorsand generators, and, more particularly, to electrical machines havinghybrid rotors, i.e., both electric and permanent magnet excitation.

2. The Prior Art

Lundell-type electrical machines are well-known in the art. For example,Lundell-type electrical generators have long been used in the automotiveindustry to provide electrical power for automobiles and trucks. Due toconsumer demand for power consuming convenience and luxury items, suchas high-powered sound systems, power windows, and the like, as well asthe need for the complicated control systems required to meet governmentemission and safety standards, electrical demands on modern automobileshave increased substantially over the years. Although the output of aconventional Lundell-type generator can be increased to meet theincreased electrical demand, the additional electrical output comes atthe expense of additional size and weight. Since underhood space onmodern automobiles is limited, the use of a physically larger generatorto meet a vehicle's increased electrical demands might not be anacceptable design solution in some cases. Further, as vehicle weightincreases, fuel economy and performance decrease.

An electrical generator's output can be increased without a proportionalincrease in size and weight by using a permanent magnetic field tosupplement the conventional electrically-generated rotor field. U.S.Pat. Nos. 4,959,577 and 5,483,116 disclose hybrid Lundell-typegenerators having a plurality of discrete permanent magnet segmentslocated between the interleaved fingers of the rotor claw segments.However, the designs disclosed by the foregoing references involvecomplicated arrangements of magnets and magnet holders, thus making thegenerator difficult to assemble.

It would be desirable to provide an electrical generator which provideshigh specific output, using proven design principles, in a relativelylightweight, compact, easy-to-assemble package.

SUMMARY OF THE INVENTION

The invention is a hybrid Lundell-type electrical machine characterizedby a rotor whose magnetic field is established using one or moreconventional field coils and one or more permanent magnets.

A conventional Lundell-type generator rotor includes a bobbin-woundfield coil mounted on a rotor shaft to generate a magnetic field. Themagnetic field flux is transferred through two claw-type rotor segmentsforming the north and south poles, respectively, of the magnetthus-created. The magnetized rotor assembly spins inside a stator havinga number of windings which are “cut” by the magnetized rotor's fluxlines so as to induce an electrical current in the stator windings.

The output of a Lundell-type generator is a function of the rotormagnetization, among other parameters. Rotor magnetization is a functionof the magnetic field strength in the rotor, which, in turn, is afunction of the field coil excitation current. That is, by increasingthe field coil excitation current, and thereby increasing the inducedmagnetic field strength in the claw segments, the rotor magnetizationcan be increased. However, the magnetization of the claw segments can beincreased only up to a certain level, based on the size and materialcomposition of the claw segments, beyond which the claw segments becomemagnetically saturated. Once the claw segments become saturated, theirmagnetization does not continue to increase with increased magneticfield strength. Therefore, as a practical matter, the maximum rotormagnetization in a conventional Lundell-type generator is a function ofthe rotor's size and, more particularly, the claw segments' size.

Permanent magnets can be used in lieu of a field coil to magnetize agenerator rotor, and they can provide greater rotor magnetization than afield coil of comparable size. However, the output voltage of agenerator using only a permanent magnet to establish rotor magnetizationis not easily controlled.

The present invention is directed to a hybrid electrical machine whoserotor magnetization is established using a combination of one or moreelectrically excitable field coils and one or more permanent magnets;the remainder of the machine may be conventional. The permanent magnetprovides a base level of rotor magnetization. The rotor's magnetizationcan be increased above the base level of magnetization provided by thepermanent magnet, subject to the limitations discussed above, byelectrically exciting the field coil. Since a permanent magnet of agiven size can effect a greater level of rotor magnetization than afield coil/claw segment assembly of the same size, a hybrid rotoraccording to the present invention can achieve a higher level ofmagnetization than a conventional rotor of the same size. Alternatively,a hybrid rotor according to the present invention having a predeterminedlevel of magnetization can be smaller and lighter than a conventionalLundell-type generator rotor having the same level of magnetization.

A first embodiment of a hybrid rotor according to the present inventioncomprises an otherwise conventional Lundell-type generator rotor (i.e.,a rotor shaft having a field coil and two claw segments, each clawsegment having a plurality of axially-extending fingers) having one ormore radially-magnetized permanent magnets located about the peripheryof each of the claw segments. In a preferred embodiment, a ring magnetis provided for each claw segment (i.e. each hybrid rotor includes tworing magnets). In an alternate first embodiment, a plurality of discretemagnets may be used in place of one or both of such ring magnets. In anycase, the magnet or magnets associated with each claw segment have anumber of magnetic poles equal to twice the number of fingers associatedwith the respective claw segment.

In a second embodiment of the invention, the hybrid rotor includes firstand second claw segments mounted on a shaft, as would a conventionalLundell-type generator rotor. The rotor further includes a third clawsegment located between the first and second claw segments. The thirdclaw segment has fingers extending axially in both directions, towardsboth the first and second claw segments, such that the fingers of thethird claw segment are interleaved with the fingers of the first andsecond claw segments. A first field coil is located between the firstand third claw segments and a second field coil is located between thesecond and third claw segments. One or more permanents magnets arelocated about the periphery of the first and second claw segments, inthe same manner as discussed above for the first embodiment. In analternate second embodiment, one or more permanent magnets are locatedabout the periphery of the third claw segment, but not the first andsecond claw segments. In another alternate second embodiment, one ormore permanent magnets are located about the periphery of the first,second, and third claw segments.

In a third embodiment of the invention, the hybrid rotor includes firstand second claw segments mounted on a non-magnetic shaft. The rotorfurther includes a third claw segment located between the first andsecond claw segments. The third claw segment has fingers extendingaxially in both directions, towards both the first and second clawsegments, such that the fingers of the third claw segment areinterleaved with the fingers of the first and second claw segments. Afirst field coil is located between the first and third claw segments,and an axially-magnetized permanent magnet comprising a ring magnet or aplurality of discrete magnets is located between the second and thirdclaw segments. In an alternate third embodiment, one or moreradially-magnetized permanent magnets also may be located about theperiphery of the first, second, and/or third claw segments.

This application is being filed contemporaneously with related U.S.patent application Ser. No. 09/650,334 entitled “Hybrid ElectricalMachine with Axial Flux Magnet,” and related U.S. patent applicationSer. No. 09/649,306 entitled “Hybrid Electrical Machine with AxiallyExtending Magnets,” both of which are owned by common assignee DelphiTechnologies, Inc.

Additional advantages and features of the present invention will becomeapparent from the reading of the attached description and the followingset of drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a conventional prior art Lundell-typegenerator rotor;

FIG. 2 is a perspective view of a first embodiment of a hybrid generatorrotor according to the present invention;

FIG. 3 is a perspective view of a second embodiment of a hybridgenerator rotor according to the present invention;

FIG. 3a is a perspective view of a variation of the second embodiment ofa hybrid generator rotor according to the present invention;

FIG. 4 is a perspective view of a variation of a second embodiment of ahybrid generator rotor according to the present invention;

FIG. 5 is a perspective view of another variation of a second embodimentof a hybrid generator rotor according to the present invention;

FIG. 6 is a perspective view of a further variation of a secondembodiment of a hybrid generator rotor according to the presentinvention;

FIG. 7 is a perspective view of a third embodiment of a hybrid generatorrotor according to the present invention; and

FIG. 7a is a perspective view of a variation of the third embodiment ofa hybrid generator rotor according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a conventional Lundell-type generator rotor 20. Rotor20 comprises a shaft 22, a field coil 24, a first claw segment 26, and asecond claw segment 28. Field coil 24 is mounted on shaft 22 betweenfirst and second claw segments 26 and 28, respectively.

FIG. 2 illustrates a first preferred embodiment of a hybrid generatorrotor according to the present invention. Hybrid rotor 120 comprises ashaft 122, a field coil 124, a first claw segment 126 and a second clawsegment 128. Field coil 124 is located on shaft 122 between first andsecond claw segments 126 and 128. Each of first and second claw segments126 and 128 includes a plurality of axially extending fingers 126′ and128′. Fingers 126′ of first claw segment 126 are interleaved withfingers 128′ of second claw segment 128, so as to substantiallyencapsulate field coil 124. Each of first and second claw segments 126and 128 also includes an axially-extending shelf 127 and 129,respectively, which acts as a support and magnetic backiron for one ormore permanent magnets. In a preferred embodiment, a radially-magnetizedring magnet having a number of poles equal to twice the number of clawfingers 126′ or 128′ on claw segments 126 and 128, respectively, ismounted on each shelf 127 and 129. In other embodiments, either or eachof ring magnets 130 may be replaced with a plurality ofradially-magnetized discrete magnets, such as a plurality of bar magnets(see FIG. 3A). In any case, the ring magnet 130 or the plurality of barmagnets (see FIG. 3A) associated with each claw segment 126, 128 has anumber of magnetic poles equal to twice the number of fingers associatedwith the respective claw segment 126, 128.

FIG. 3 illustrates a second embodiment of a hybrid generator rotoraccording to the present invention. Hybrid rotor 220 comprises a shaft222, a first claw segment 226, and a second claw segment 228. Hybridrotor 220 further includes a third claw segment 232 which is locatedbetween first and second claw segments 226 and 228. First claw segment226 has a plurality of axially-extending fingers 226′ and second clawsegment 228 also has a plurality of axially-extending fingers 228′.Third claw pole segment 232 has a first plurality of axially-extendingfingers 232′ and a second plurality of axially-extending fingers 232″. Afirst field coil 224 is located between first claw pole segment 226 andthird claw pole segment 232, such that first field coil 224 issubstantially encapsulated by claw fingers 226′ and 232′. A second fieldcoil 234 is located between second and third claw pole segments 228 and232, such that second field coil 234 is substantially encapsulated byclaw fingers 228′0 and 232″.

Each of first and second claw segments 226 and 228 also includes anaxially-extending shelf 227 and 229, respectively, which acts as asupport and magnetic backiron for one or more permanent magnets. In apreferred embodiment, a ring magnet 230 is mounted on each shelf 227 and229. In other embodiments, either or each of ring magnets 230 may bereplaced with a plurality of discrete magnets, such as a plurality ofbar magnets, mounted on axially-extending shelves 227 and 229. In anycase, the ring magnet 230 or the plurality of bar magnets 225 shown inFIG. 3A associated with each claw segment 226, 228 has a number ofmagnetic poles equal to twice the number of fingers associated with therespective claw segment 226, 228.

FIG. 4 illustrates a variation of the foregoing second embodimentwherein rotor 220 comprises third claw segment 232 is provided with acircumferential channel 233 about its periphery. In a preferredembodiment, a ring magnet 231 is mounted within channel 233. In analternate embodiment, ring magnet 231 may be replaced with a pluralityof discrete magnets, such as a plurality of bar magnets (not shown),mounted within channel 233 about the periphery of claw segment 232. Inanother alternate embodiment, third claw segment 232 may be splitaxially into two sections 232A and 232B, each having anaxially-extending shelf 233A and 233B, respectively, wherein ring magnet231 is mounted on axially-extending shelves 233A and 233B. See FIG. 5.

FIG. 6 illustrates another variation of the foregoing second embodimentwherein third claw segment 232 is provided with a circumferentialchannel 233 about its periphery and wherein one or more permanentmagnets, such as ring magnet 231, are mounted within channel 233, butwherein first and second claw segments 226 and 228 do not have anypermanent magnets associated therewith. Accordingly, in this embodiment,first and second claw segments 226 and 228 preferably lack theaxially-extending shelves 227 and 229 provided in those embodimentswherein permanent magnets are associated with first and second clawsegments 226 and 228, as shown in, for example, FIGS. 3 and 4.

FIG. 7 illustrates a third embodiment of a hybrid generator rotoraccording to the present invention. Hybrid rotor 320 comprises anon-magnetic shaft 322, a first claw segment 326, and a second clawsegment 328. Hybrid rotor 320 further includes a third claw segment 332which is located between first and second claw segments 326 and 328.First claw segment 326 has a plurality of axially-extending fingers 326′and second claw segment 328 also has a plurality of axially-extendingfingers 328′. Third claw pole segment 332 has a first plurality ofaxially-extending fingers 332′ and a second plurality ofaxially-extending fingers 332″. A first field coil 324 is locatedbetween first claw pole segment 326 and third claw pole segment 332,such that first field coil 324 is substantially encapsulated by clawfingers 326′ and 332′. In a preferred embodiment, an axially-magnetizedring magnet 336 is located between second and third claw segments 328and 332, such that ring magnet 336 is substantially encapsulated by clawfingers 328′ and 332″. There may also be a combination of a ring magnetand a soft magnetic material axial spacer in the same space occupied bythe ring magnet alone in FIG. 7, as is shown in FIG. 7a, which hasspacer 329 below ring magnet 336. In other embodiments, a plurality ofaxially-magnetized discrete magnets, such as a plurality of bar magnets225, as seen in FIG. 3a, may replace ring magnet 336. In variations ofthe third embodiment (not illustrated), one or more permanent magnetsalso may be located about the first, second, and/or third claw segments326, 328, and 332, in the manner shown in FIGS. 3, 4, and 5.

The foregoing disclosure is intended merely to illustrate certainpreferred embodiments of the invention. It is contemplated that thoseskilled in the art may find numerous ways to modify these embodimentswithout departing from the scope and spirit of the invention. As such,the scope of the invention is defined by the appended claims and not bythe details of the specification.

I claim:
 1. A rotor for an electrical machine, comprising: a pair offield coils being encased by a pair of claw pole segments and a centersection, each of said claw pole segments having a plurality of claws forintermeshing with a plurality of claws of said center section; and aplurality of magnets being disposed on said center section, saidplurality of magnets being of alternating polarity and being configuredto align with said plurality of claws.
 2. The rotor as in claim 1,wherein said plurality of magnets is a ring magnet configured to have aplurality of alternating poles.
 3. The rotor as in claim 2, wherein saidcenter section comprises a pair of center sections each having aplurality of claws at one end and an axially extending shelf portion atthe other end, said plurality of claws of one of said pair of saidcenter sections being configured to intermesh with said plurality ofclaws of one of said pair of claw pole segments and the plurality ofclaws of the other one of said pair of center sections being configuredto intermesh with said plurality of claws of the other one of said pairof claw pole segments, said axially extending shelf portions of saidpair of said center sections being configured to define a channel forreceiving said ring magnet.
 4. The rotor as in claim 3, wherein saidaxially extending portions provide a magnetic backiron for said ringmagnet.
 5. The rotor as in claim 2, wherein said ring magnet is receivedwithin a channel disposed on said center section.
 6. The rotor as inclaim 5, wherein the number of alternating poles is twice the number ofsaid plurality of claws in either of said pair of claw pole segments. 7.The rotor as in claim 1, wherein said center section is twice the sizeof one of said pair of claw pole segments.
 8. A rotor for an electricalmachine, comprising: a first field coil; a second field coil; a firstclaw pole segment having a plurality of claws partially encasing saidfirst field coil; a second claw pole segment having a plurality of clawspartially encasing said second field coil; a center segment having acenter section, a first plurality of claws and a second plurality ofclaws, said first plurality of claws depending outwardly from saidcenter section and being configured to interlock with said plurality ofclaws of said first claw pole segment, said second plurality of clawsdepending outwardly from said center section and being configured tointerlock with said plurality of claws of said second claw pole segment;and a ring magnet disposed in a channel in said center segment.
 9. Therotor as in claim 8, wherein said ring magnet is configured to have aplurality of poles of alternating polarity, said plurality of polesbeing aligned with said first plurality of claws, said second pluralityof claws and the plurality of claws of said first claw pole segment andsaid second claw pole segment.
 10. The rotor as in claim 8, wherein saidcenter section of said center segment provides a surface area disposedbetween said first plurality of claws and said second plurality ofclaws.
 11. The rotor as in claim 10, wherein said channel is disposed insaid surface area and said ring magnet is configured to have a pluralityof poles of alternating polarity, said plurality of poles being alignedwith said first plurality of claws, said second plurality of claws andthe plurality of claws of said first claw pole segment and said secondclaw pole segment.
 12. The rotor as in claim 8, wherein said centersegment comprises a first center section and a second center section,said first center section having a first plurality of claws at one endand an axial shelf at the other end, said second center section having asecond plurality of claws at one end and an axial shelf at the otherend, said first plurality of claws depending outwardly from said centersegment and being configured to interlock with said plurality of clawsof said first claw pole segment, said second plurality of clawsdepending outwardly from said center segment and being configured tointerlock with said plurality of claws of said second claw pole segment;a channel being defined by said axial shelf of said first center sectionand said axial shelf of said second center section; and a ring magnetdisposed in said channel.
 13. The rotor as in claim 12, wherein saidring magnet is configured to have a plurality of poles of alternatingpolarity, said plurality of poles being aligned with said firstplurality of claws, said second plurality of claws and the plurality ofclaws of said first center section and said second center section. 14.The rotor as in claim 13, wherein said ring magnet being configured toincrease the magnetic field strength of the rotor.
 15. A method forincreasing the power density of an electric machine, comprising:locating a pair of electrically excitable field coils about a shaft;encasing one of said pair of field coils with a first pair ofinterlocking claws and encasing the other one of said pair of fieldcoils with a second pair of interlocking claws; disposing a plurality ofmagnets between said first and second pairs of interlocking clawswherein said plurality of magnets increase the magnetic fields generatedby said pair of field coils.
 16. The method as in claim 15, wherein thenumber of said plurality of magnets is equal to the number ofinterlocking claws encasing one of said pair of field coils.
 17. Themethod as in claim 15, wherein the poles of said plurality of magnetsare positioned in an alternating fashion and are configured to alignwith said claws encasing said pair of field coils.